Class FeederChainGoal

Objects of this class are used for production chains on feeder islands
The update call reserved the production for the (non-existent) settlement
so it can't be transferred. The late_update call declares that the
settlement doesn't need it after all thus freeing it. TODO: make that a
single explicit action: right now import quotas are deleted by the first
step which can make it look like less resources can be imported.